Method of removing solids (e.g. copper dross) from molten-lead baths

ABSTRACT

Layers of substantially solid fine-grained material formed on a molten-lead bath, e.g. in the refining of lead and consisting substantially of copper dross, are removed in accordance with the invention by pneumatic evacuation of the layers after they have been loosened mechanically or pneumatically, e.g. by a beater or an air blast.

'United States Patent Manthey et al.

Dec. 2, 1975 METHOD OF REMOVING SOLIDS (E.G. COPPER DROSS) FROM MOLTEN-LEAD BATHS Inventors: Peter Manthey, Krefeld-Bockum;

Hermann Matthies, Angermund, both of Germany Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed: Sept. 21, 1973 Appl. No.: 399,511

Assignee:

Foreign Application Priority Data Sept. 29, 1972 Germany 2247737 US. Cl 75/78; 75/24; 75/93 R Int. Cl. C22B 13/06 Field of Search 75/78, 93 R, 69, 25, 24;

[56] References Cited UNITED STATES PATENTS 3,632,096 l/l972 Perry 266/37 FOREIGN PATENTS OR APPLICATIONS 465,345 4/1937 United Kingdom 75/78 4547066 12/1970 Japan 75/93 Primary Examiner-M. J. Andrews Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT Layers of substantially solid fine-grained material formed on a molten-lead bath, e.g. in the refining of lead and consisting substantially of copper dross, are removed in accordance with the invention by pneumatic evacuation of the layers after they have been loosened mechanically or pneumatically, e.g. by a beater or an air blast.

2 Claims, 4 Drawing Figures US. Patent Dec. 2, 1975 Sheet 1 of 2 3,923,499

US. Patent Dec. 2, 1975 Sheet 2 of2 3,923,499

F ILT'EE CYCLONE SUCTION BLOWER ROTA TOR SUPPER -01?! VE MOTOE METHOD OF REMOVING SOLIDS (E.G. COPPER DROSS) FROM MOLTEN-LEAD BATHS FIELD OF THE INVENTION The present invention relates to a method of removing solid layers overlying molten-lead baths, e.g. in the refining of lead.

BACKGROUND OF THE INVENTION In metallurgical processes involving the formation of molten-lead baths, fine-grained solid layers are frequency formed on the lead bath and have a high bulk density. These layers must be removed and various devices have been provided for this purpose. For example, fine-grained copper dross collects on the surface of a lead bath in the refining of crude lead in the form of a crust or other relatively stiff layer and may be removed by perforated scoops, by foam methods and simply by skimming the solids from the bath.

Prior-art processes have, however, the disadvantages that the solids are not sufficiently removed from the bath and the method of removal frequently is unhygienic. Furthermore, large losses of lead may occur and the cost of removal of the solids may be prohibitive.

OBJECTS OF THE INVENTION It is the principal object of the present invention to provide a method of removing solids from baths of a liquid, especially a hot liquid such as a molten metal, whereby the aforementioned disadvantages are avoided, i.e. the solids may be removed without significant removal of the liquid phase at relatively low cost and in a hygienic manner.

Another object of the invention is to provide a method of removing copper dross from a molten-lead bath wherein the removal is relatively efficient and complete and does not adversely affect the economics of a lead-refining process.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, by the simultaneous loosening of the crust overlying a layer of molten metal or other liquid phase and inducing the loosend crust or solid to pass into a duct pneumatically, e.g. under suction. In other words, the invention comprises loosening the layers of solid material upon a liquid bath and simultaneously drawing the loosened solid material off the surface of the bath pneumatically by suction.

According to a feature of the invention, the solids are loosened mechanically, e.g. by mechanically disturbing the surface layer or crust with a rotating beater such as a beating rod, chain, roll or blade wheel having horizontally extending axes and radially projecting or outwardly projecting members or tines which engage the layer of solids or crust. Alternatively, the loosening step may be carried out pneumatically, i.e., by directing jets of gases under pressure against the crust or layer, preferably between the crust or solid layer and the liquid phase, i.e., at the interface between the solid and liquid phases. The gases which are used are preferably heated to avoid cooling of the liquid phase, i.e., the molten lead.

Preferably the solids are drawn off under suction simultaneously with loosening and mechanical breakup of the crust by a gas stream and are classified or separated by particle size or content. The latter separation may be accomplished by a cyclone and a bag filter provided downstream of the cyclone. When copper dross is removed from the surface of a lead bath, the dust collected in the cyclone has a relatively high copper content while the dust collected in the bag filter has a high tin content. The products recovered from the two classification stages may then be supplied to further processing operations, e.g. a copper-recovery and a tinrecovery process.

We have found it to be advantageous to provide means whereby secondary air may be introduced at a controlled rate into the gas stream or duct entraining the solids drawn off the surface of the molten-metal bath to enable a cooling of the stream of entraining air so that the temperature permissible in the succeeding dust filters will not be exceeded. The rate of secondaryair intake is controlled so that the suction action at the surface of the bath is not diminished to the point that the solids are not drawn into the hood or nozzle forming the intake of the suction device.

The apparatus for carrying out the present invention thus advantageously comprises a hood provided with an elongated opening at least on one longitudinal side, a suction conduit disposed above the opening and connected to the hood, and crust-loosening means within the opening or disposed adjacent the latter for loosening the solid layer or crust upon. the surface of the molten-metal bath. The loosening means may be disposed ahead of or in the opening or within the hood and, at any rate, are preferably connected therewith.

Advantageously, the underside of the hood is open and the edges around the opening are sealed by the layer of solids and/or by the bath of molten metal. Where the loosening means consist of rotating beaters, the beaters such as beating rods, chains, rolls, horizontally arranged blade wheels and the like, are disposed approximately along the longitudinal dimension of the opening. The direction of rotation of the beaters is selected, so that the solids are loosened toward and are displaced by the beaters in the direction of the opening.

Preferably the hood walls extend at right angles to the surface of the molten material and the interface between the solid layer or crust and the molten bath. This configuration has been found to yield an especially effective separation as the solids are entrained in the gas stream directly upwardly while entrainment of liquid particles is avoided to a considerable degree. An airflow control disk may be incorporated in the vacuum duct so that the secondary air for controlling the temperature of the entrainin g gas stream can be introduced at a controlled rate, Le, a rate which does not adversely affect the solids-entraining suction at the openmg.

To draw off the solid layer, the suction head may be moved over the stationary crust or solid layer or the solid layer may be moved on the bath past a stationary suction head below the latter. lln the first case, means may be provided for sweeping the suction head over the surface of the bath while, in the latter case, means may be provided for displacing the bath. Such means may include stirring devices and the like. Of course, both a head-displacement and a bath-displacement means may be utilized.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic perspective view showing a suction head in accordance with the present invention, provided with rotating beaters, for loosening the crust or solid material immediately ahead of the opening;

FIG. 2 is a view similar to FIG. 1 of a suction head using a pneumatic crust-loosening device;

FIG. 3 is a transverse sectional view, in diagrammatic form, showing a suction head in conjunction with rotatable beater rods disposed in the hood; and

FIG. 4 is a vertical cross-section, partly in diagrammatic form, illustrating still another feature of the invention.

SPECIFIC DESCRIPTION In FIG. 1 we have shown a hood 2 having a longitudinal side 1 provided with an elongated opening 3 along a layer of solid material or crust disposed upon a bath of molten lead. A suction conduit 5 opens at the top of the upwardly convergent head within the latter and loosening means 6a is disposed immediately ahead of the opening 3 or within the latter. The means for mounting the beater 6a upon the hood are not shown nor have we illustrated the 'means for driving the beater. Such means may be identical to those illustrated in connection with FIG. 3.

The loosening means 6a comprises a plurality of angularly spaced radially extending beating vanes and rotate in the direction of the arrow, i.e., in the clockwise sense as seen in FIG. 1.

When the hood 2 etc. is displaced across the bath or the bath is displaced relative to the stationary hood, the beater 6a loosens the cooper dross crust or layer on the molten lead and the broken-up solids are withdrawn by suction through conduit 5.

In the embodiment of FIG. 2, where reference numerals identical to those used in FIG. 1 represent similar structural elements, the loosening means 6b comprises a pipe formed with holes directed toward the opening 3 and forming nozzles for air jets which are inclined somewhat downwardly so that the air jet is directed at the interface between the solid crust and the moltenlead bath. The pneumatic jet from nozzle pipe 6b thus lifts the crust and breaks the same into small pieces which are withdrawn by suction as described in connection with FIG. 1. Heating means H is connected to the duct 6b feeding the loosening air to the nozzle pipe 6b so as to prevent excessive cooling of the molten metal at the interface at which the loosening jets impinge.

In FIG. 3, wherein reference numerals similar to those of FIGS. 1 and 2 are again used to illustrate similarly functioning parts, the loosening means 6a consists of beating rods mounted in the hood 2. The entire hood is mounted in the holder 7 and by means of a rope drive anchored at 8 to the system can be raised and lowered toward the surface of the melt. A frame 9 supports the apparatus over the molten material and a motor 10 on this frame drives the beating drum 60 via a chain 11. An inspection door is provided at 12 to permit the beater 6a to be viewed and an air-control disk 13 permits induction of limited quantities of secondary air for cooling the primary airstream. The system of FIG. 3, of course, operates in the manner previously described.

In FIG. 4, we have shown an embodiment of the invention which makes use of a suction hood 29 of any of the type shown in FIGS. 1-3. In this embodiment, the

molten lead 21 is received in a vat 20 and may be rotated or stirred by a plurality of paddles 23 and 24 mounted upon a stirring rod or shaft 22 which is driven by a speed-reduction transmission 25 from a stirrerdrive motor 26. A copper-dross layer 28 overlies the upper surface 27 of the lead bath and is drawn into the hood 29 which is provided with a beater or pneumatic crust-loosening device as previously described.

The hood 29 is carried by a suction duct 30 which is rotatable about the axis of the vat in a bearing 31 by a transmission 32 of a hood-rotating motor 33. A distributor 34 on a stationary pipe 35 communicates with the rotatable duct 30 to maintain suction therein. The pipe 35 opens tangentially into a cyclone separator 36 from which the gas is withdrawn via line 37 into a bag filter 38 connected to a suction blower 39. The system of FIG. 4 operates as described in connection with FIGS. 13 except that rotation of the hood or of the bath serves to bring the solid layer into the hood opening for evacuation with the gas stream.

SPECIFIC EXAMPLE Using a stationary suction apparatus as shown in FIG. 3, 5.5 metric tons of dry copper dross, which wasas fine as dust, was evacuated within a period of three hous from a constantly stirred melting vessel containing molten lead at a temperature of about 500C. The vessel had a diameter of 3.6 meters and contained approximately metric tons of the molten lead. The hood had a length and width of 55 X 48 cm and an opening 3 with a height of 10 cm over the entire length of the hood. The beater drum 6a had a diameter of 40 cm and was rotated at a speed of 50-70 RPM. Air is drawn off at a rate of I00 m /min. (STP) and contained g of dust per rn (STP) at a temperature of l50-200C. The airflow in the vacuum conduit had a velocity of 15 20 m/sec. As illustrated in FIG. 4, the evacuated dust was separated in a cyclone and a bag filter in succession. About 95 percent of the evacuated dust was recovered in the cyclone and the remaining 5 percent was recovered from the bag filter. The dust collected in the cyclone contained about 27 percent copper and about 2.5 percent tin while the dust collected in the bag filter contained 3 percent copper and 11 percent tin. The cyclone dust was supplied directly to a process for the recovery of copper while tin was recovered from the dust collected in the bag filter. Approximately 55 kg of dross containing 27 percent copper were collected per metric ton of lead.

By comparison, the dross recovery using perforated scoops withdraws about 74 kg of material containing only 20 percent copper per metric ton of lead. Because the dross is collected at a lower rate and with a higher copper content according to the present invention, the costs of handling of processing the dross are substantially reduced. The solid separation is carried out with low-labor cost and yields high-grade products. Losses of lead are kept low and the operation can be performed under hygienic conditions. A single-operation separation is another advantage.

We claim:

1. A process for removing a layer of substantially fine-grain solid material formed by refining and consisting of copper dross upon a bath of molten lead, comprising the steps of:

loosening said layer by mechanically disturbing it with a rotary beater extending into the copper dross on the surface of the bath and simultaneously sucking the loosened layer of solid material off 2. The process defined in claim l,further comprising from the bath directly upwardly in a gas stream by the step of admitting secondary air at a controlled rate evacuation, and separating the solids from the gas into the evacuating gas stream containing the evacustream in a filter device. ated solids. 

1. A PROCESS FOR REMOVING A LAYER OF SUBSTANTIALLY FINE-GRAIN SOLID MATERIAL FORMED BY REFINING AND CONSISTING OF COPPER DROSS UPON A BATH OF MOLTEN LEAD, COMPRISING THE STEPS, OF: LOOSING SAID LAYER BY MECHANICALLY DISTRUBING IT WITH A ROTARY BEATER EXTENDING INTO THE COPPER DROSS ON THE SURFACE OF THE BATH AND SIMULTANEOUSLY SUCKING THE LOSSENED LAYER OF SOLID MATERIAL OFF FROM THE BATH DIRECTLY UPWARDLY IN A GAS STREAM BY EVACUATION, AND SEPARATING THE SOLID FROM THE GAS STREAM IN A FILTER DEVICE.
 2. The process defined in claim 1, further comprising the step of admitting secondary air at a controlled rate into the evacuating gas stream containing the evacuated solids. 